For example, in a high-frequency power amplifier that amplifies a high frequency signal such as a microwave or a millimeter wave, in order to maximally bring out the capability of a transistor that amplifies the high frequency signal, i.e., in order to bring out the maximum output characteristics and the maximum efficiency characteristics of the transistor, a transformation of the impedance from the external load to the transistor is performed using a matching circuit.
Concretely, the design of the matching circuit is performed in such a way that a designed value (referred to as a “design impedance” hereafter) of the impedance when the matching circuit is viewed from the connection point between the matching circuit and the transistor matches a load impedance which is determined using a load pull measurement or the like and at which the maximum characteristics of the transistor are acquired.
The matching circuit is usually constituted of a matching circuit board in which a pattern is formed on a dielectric board by using metal wiring.
However, in the high-frequency power amplifier, there is a case in which due to either variations in the assembly of matching circuit boards and wires connecting the matching circuit boards, or the occurrence of a mismatch between the design impedance and the load impedance which is caused by a change of the characteristics of the transistor itself, the capability of the transistor cannot be brought out maximally. There is, in addition to a case in which the characteristics of the transistor itself change due to non-intended variations in the characteristics, a case in which the characteristics change with a change of the specifications, or the like.
A high-frequency power amplifier including, as a means for compensating for this mismatch between the design impedance and the load impedance, an output matching circuit comprised of an open stub whose line length is variable depending on the presence or absence of connection of a wire to an island pattern, and a line having a length of one-quarter wavelength at the frequency of the fundamental wave of a high frequency signal is disclosed in the following Patent Literature 1.
In this high-frequency power amplifier, an adjustment of the design impedance is performed by changing the number of wires connected for an island pattern disposed close to an output matching circuit pattern.